public class Square extends Graphic{
    public  double getPeri() {return 4 * _lengh;}
    public  double getAera() {return _lengh * _lengh;}

    public Square(double _lengh) {
        this._lengh = _lengh;
    }

    public double get_lengh() { return _lengh; }
    public String getMessage()
    {
        return "正方形，边长是：" + _lengh + " 面积是：" + getAera() + " 周长是：" + getPeri();
    }
    private double _lengh;
}
